CD4 counts are used to determine eligibility to initiate ART and to monitor response.(1, 2, 3, 4, 5) In sub-Saharan Africa, there remain a large number of persons in need of ART but insufficient laboratory support for CD4 testing. CD4 testing is particularly challenging in rural areas. Low-cost point-of-care (POC) tests are increasingly popular and are currently the standard of care in the region for HIV testing.

Objective

To evaluate the performance of the PIMA POC CD4 test system against standard, laboratory testing.

Setting

A voluntary HIV counseling and testing center in Harare, Zimbabwe.

Study Design

Cross-sectional.

Participants

Men and women who tested HIV-positive at a voluntary counseling and testing (VCT) site.

Participants were recruited during post-test counseling and after consent was obtained provided 1-2 drops of blood obtained by finger stick for testing with the PIMA POC system. Participants then provided a serum specimen obtained by venipuncture for standard CD4 testing. Half of the subjects had their POC testing performed by nurses and the other half by laboratory technicians. Both nurses and technicians were VCT staff who routinely conducted the rapid HIV tests. Participants were provided with only the CD4 test results obtained from standard testing. These were available within 2-3 days. CD4 test results from the POC system and standard CD4 testing were linked with a unique study identification number. Different technicians performed the standard CD4 testing and the POC testing. Standard CD4 testing was performed at the National Microbiology Reference Laboratory at Harare Central Hospital.

Accuracy of the PIMA system compared to standard CD4 testing was done using the Bland-Altman method. Misclassification of ART eligibility was done by comparing the percentage of patients who would be misclassified as being either below or above ART eligibility CD4 thresholds (200 and 350 cells/µL) using the POC system compared with results from standard testing.

Results

There were 165 participants; 74 men and 91 women. The mean age was 37.4 years among men and was 35.1 years among women. The number of participants tested by nurses and by technicians was similar (84 and 81 respectively).

The mean bias of the PIMA device was +7.6 cells/µL relative to the FACSCalibur (95% CI: -6.6, 21.8; p=0.72). The bias at values <400 cells/µL was +8.6 cells/µL (95% CI: -2.19, 19.2; p=0.54) and for values >400 cells/µL was +2.4 cells/µL (95% CI: -51.8, 56.6; p=0.96). The performance of technicians and nurses did not differ (p=0.15).

At an ART initiation threshold of 200 cells/µL, 2.4% of participants were misclassified above this threshold using the PIMA system compared with the FACSCalibur, whereas 4.2% were misclassified below the threshold. Using a threshold of 350 cells/µL, 4.2% of participants were misclassified above the threshold, and 2.4% of participants were misclassified as below the threshold.

Conclusions

The PIMA POC testing system produced CD4 counts that were similar to the results obtained from standard CD4 testing. POC testing at VCT is feasible.

Quality Rating

This was a well conducted study. The sample size was sufficiently large to detect statistically significant differences in the testing methods. The participants are likely to be representative of the target population. The study was conducted in an urban VCT site and as such, it is not clear how acceptable and feasible use of POC CD4 testing will be in rural areas.

Programmatic Implications

CD4 counts are necessary for clinical staging and initiation and monitoring of ART. The need for flow cytometry to measure CD4 counts has been a barrier to its use in rural areas and results in delays in receipt of results. POC testing provides a practical approach to address the current problems with CD4 testing. The results of this study provide evidence in support of POC CD4 testing. An important limitation to the PIMA system is that it does not measure CD4% and therefore, cannot be used for clinical staging or monitoring in children. Additional tests with the PIMA and other systems in rural areas are necessary before widespread use in these settings.